The low pressure turbine of an aviation turbomachine is made up of a plurality of stages, each stage including a nozzle (i.e. a grid of stationary guide vanes) and a rotor wheel placed behind the nozzle.
Typically, a low pressure turbine rotor is made up of a rotor disk provided at its periphery with slots in which the roots of the blades are engaged. An annular plate fastened to the rotor disk serves to hold the blades axially on the disk.
At present, it is common practice to replace the metal blades of such a rotor with blades that are made of composite material, while the rotor disk continues to be made of metal.
The use of a composite material for making blades is justified by the very good behavior of composite materials at the high temperatures to which blades are subjected, and also to their lower density (where composite materials present a density that is divided by about 3.5 relative to the density of the metal).
Nevertheless, having recourse to composite materials for making the blades of a gas turbine rotor wheel raises the problem of holding them in the slots of the disks. In operation, differences of expansion between the disk (made of metal) and the blades (made of composite material, in particular ceramic matrix composite (CMC) material) can give rise to contact being lost at the bearing surfaces of the blade roots. Under such circumstances, this loss of contact can lead to a blade tilting in the slot about a direction that is parallel to the central axis of symmetry of the turbomachine.
It is known to have recourse to a spacer placed between the bottom of the slot and the inner face of the blade root.
Document FR 2 918 129 provides for having recourse to a spacer of elastically deformable material with a longitudinal segment presenting a transverse profile of arcuate shape.
Nevertheless, such a spacer does not always manage to oppose sufficiently the above-mentioned tilting movements between the blade root and the corresponding slot.
In addition, having recourse to a spacer presents several drawbacks, including the fact of being expensive and of requiring each spacer to be made to measure, which is not compatible with mass production. It is necessary to adapt and fit the dimensions of each spacer to its future location as a function of the shape presented by the pair constituted by the slot and the blade root that is associated therewith. In addition, there is a risk of assembly errors, with spacers being interchanged, and there is also a problem of spacer traceability being relatively burdensome to manage.